1. Field of the Invention
The present invention relates to a pickup drive apparatus and a pickup drive method, which perform either recording operation or reproducing operation with respect to a recording medium such as a CD and a DVD.
2. Description of the Related Art
Conventionally, in a recording/reproducing apparatus for recording/reproducing information on a recording medium (will be referred to as an xe2x80x9coptical diskxe2x80x9d hereinafter) such as a CD (Compact Disk) and a DVD (Digital Video Disk, or Digital Versatile Disk) with employment of a pickup, a tracking servo control is carried out by using a radial contrast signal by way of a pickup drive apparatus having an arrangement shown in FIG. 15 in order to properly control a position of the pickup along the radial direction.
In FIG. 15, very small spot light xe2x80x9cSPxe2x80x9d is irradiated from a pickup onto grooves xe2x80x9cGxe2x80x9d and lands xe2x80x9cLxe2x80x9d, which are alternately positioned along a radial direction xe2x80x9cxcex8rdxe2x80x9d of an optical disk, and thus, return light such as reflection light produced by this spot irradiation is detected by a photodetector 1.
In the photodetector 1, 4 light receiving units a1, a2, b1, b2 for receiving the above-described return light are provided, detection signals outputted from the respective light receiving units a1, a2, b1, b2 are added to each other by an adder 2, so that an RF signal xe2x80x9cSRFxe2x80x9d is produced. This RF signal SRF is processed by either a low-pass filter or an envelope detecting circuit 3 to thereby produce a radial control signal xe2x80x9cSRDxe2x80x9d. Furthermore, the radial control signal SRD is compared with a predetermined threshold value xe2x80x9cVREFxe2x80x9d by a comparator 4, so that a binary ON/OFF track signal xe2x80x9cSTRxe2x80x9d is produced. Then, a tracking servo control is carried out based on the ON/OFF track signal STR so as to properly control the position of the pickup in the radial direction.
FIG. 16 illustrates a principle idea of this tracking servo control. In this drawing, when the optical spot SP is moved in the same radial direction as while the optical pickup is moved along the radial direction xe2x80x9cxcex8rdxe2x80x9d, intensity of the above-described return light is changed in response to an irradiation position of the optical spot SP, and the amplitude of the radial contrast signal xe2x80x9cSRDxe2x80x9d is changed in connection to this intensity change. When this amplitude change is compared with a predetermined threshold value VREF, such an ON/OFF track signal xe2x80x9cSTRxe2x80x9d is produced, the level of which is inverted at a boundary portion between a groove xe2x80x9cGxe2x80x9d and a land xe2x80x9cLxe2x80x9d. In this ON/OFF track signal STR, a position of a groove G is indicated by a logic level xe2x80x9cHxe2x80x9d, whereas a position of a land L is indicated by a logic level xe2x80x9cLxe2x80x9d.
Then, the irradiation position of the optical spot SP with respect to the groove G corresponding to the recording track is properly controlled by performing the servo control as follows: That is, within a time period Tsink during which the ON/OFF track signal STR becomes the logic level xe2x80x9cHxe2x80x9d, such a servo control (will be referred to as xe2x80x9ctrack capturingxe2x80x9d) is carried out in order that the optical pickup is positioned at the center of the groove G. Within a time period Tout during which the ON/OFF track signal STR becomes the logic level xe2x80x9cLxe2x80x9d, such a servo control (will be referred to as xe2x80x9ctrack escapingxe2x80x9d) is performed in order that the optical pickup is shunted from the land L.
On the other hand, very recently, write-once type CD-Rs and DVD-Rs into which information can be written only once, as well as CD-RWs and DVD-RWs into which information is rewritable have been developed. However, when the tracking servo control is carried out by employing the above-described conventional pickup drive apparatus with respect to these optical disks, in the case that the above-described optical spot SP is irradiated on such an unrecorded region of the optical disk on which information is not yet recorded, both the radial contrast signal SRD and the ON/OFF track signal STR, which represent the positions of the groove G and the land L, shown in FIG. 16, cannot be obtained. Accordingly, there is such a case that the irradiation position of the optical spot SP with respect to the groove G cannot be properly controlled.
In other words, since the optical reflectivities and the diffraction characteristics with respect to the optical spot are different from each other as to the groove G on which the information is recorded (namely, recorded pit is present), and the land L, it is possible to detect the position of the groove G and the position of the land L as a difference in the respective contrast based upon both the radial contrast signal SRD and the ON/OFF track signal STR, which are obtained from the return light. As a result, the above-described proper servo control can be done. However, as to such a groove G on which no information is recorded (namely, recorded pit is not present) and the land L, when a groove interval is made narrow in order to increase the recording density, there is substantially no difference in the respective contrast. As a consequence, it is not possible to detect the position of the groove G and the position of the land L based upon the radial contrast signal SRD and the ON/OFF track signal STR. There are some cases that the above-described proper servo control cannot be carried out.
As a result, there are some cases that while the optical spot is correctly located with respect to the unrecorded groove G (positioning), the information can be hardly recorded thereon. Also, as known from a so-called xe2x80x9crandom access operationxe2x80x9d, when the pickup is moved along the radial direction with respect to the optical disk, the following difficult case may occur. That is, in this random access operation, the servo control can be quickly converged in such a manner that the pickup is moved to a desirable address area, and then the optical spot is positioned to a groove G at this address area.
The present invention has been made to solve the problems of the above-described conventional apparatus, and therefore, has an object to provide a pickup drive apparatus and a pickup drive method, capable of realizing a highly precise tracking servo control, and also a recording/reproducing apparatus equipped with such a pickup drive apparatus.
To achieve the above-described object, according to an aspect of the present invention, there is provided a pickup drive apparatus for driving/controlling a pickup used to irradiate an optical spot on a recording medium having a pre-pit between tracks, comprising: light detecting means for detecting return light produced by irradiating the optical spot; first signal producing means for producing a tracking error signal based upon the detection output of the light detecting means; second signal producing means for producing a control signal corresponding to the component of the pre-pit based upon the detection output of the light detecting means; control means for performing a tracking control in response to the tracking error signal; and supply means controlled so as to supply the tracking error signal to the control means in response to the control signal.
With employment of the above-described arrangement, the detection output containing the information of the track can be obtained by detecting the return light returned from the recording medium by the light detecting means. The first signal producing means produces the tracking error signal based upon the detection output, and this tracking error signal indicates the irradiation position of the optical spot. The second signal producing means produces a control signal corresponding to the component of the pre-pit based upon this detection output. Then, the supply means supplies the tracking error signal to the control means in response to the control signal so as to servo-control the pickup. As a result, the servo control is carried out in such a manner that the optical spot is positioned.
In particular, since the control signal is not produced based upon the difference between the contrast of the groove and the contrast of the land, which constitutes the problem of the conventional apparatus, but is produced based on the detection component of the pre-pit, such a servo control can be carried out in such a manner that the optical spot can be positioned with respect to the unrecorded groove on which the information is not recorded in high precision.
In other words, in the case that the tracking error signal is supplied to the control means in response to the control signal, when the optical spot is irradiated onto the unrecorded groove, the servo control of xe2x80x9ctrack capturingxe2x80x9d is carried out in such a manner that this optical spot is positioned to the groove. When this optical spot is irradiated onto the land, the servo control of xe2x80x9ctrack escapingxe2x80x9d is carried out in such a manner that the optical spot is moved from the land to the groove side. As a result, such a servo control is performed in order that the optical spot can be positioned on the groove in high precision.
Also, according to another aspect of the present invention, there is provided a pickup drive method for driving/controlling a pickup used to irradiate an optical spot on a recording medium having a pre-pit between tracks, comprising the steps of: detecting return light produced by irradiating the optical spot; producing a tracking error signal and a control signal corresponding to the component of the pre-pit based upon the detection output of the detecting step; and executing a tracking control by the tracking error signal in response to the control signal.
In accordance with this method, the detection output having the information of the track is obtained by detecting the return light returned from the recording medium. Based on this detection output, the tracking error signal indicative of the irradiation position of the optical spot is produced. Also, based on this detection output, the control signal is produced which is synthesized with the component of the pre-pit. Then, the servo control is carried out based on the tracking error signal in response to the control signal. As a consequence, the servo control is performed in such a manner that the optical spot is positioned to the groove.
Also, when a recording/reproducing apparatus according to another aspect of the present invention is arranged by employing the above-described pickup drive apparatus, it is possible to realize such a recording/reproducing apparatus capable of performing the above-described tracking servo in high precision.